1. Field of the Invention
The present invention relates, in general, to electrodes used in the measurement of bio-potential signals produced by living bodies and more particularly to high-impedance electrodes for transferring bio-potential signals from the body to output and/or recording devices without special skin preparation or use of electrolyte gels.
2. Background of the Invention
Various tissues exhibit electrical activity resulting in bio-electric signals that travel throughout the body. The purpose of this signal transmission is to distribute information from one part of the body to another when a necessary function is being carried out. For example, tissues such as nerves, sensory organs, and muscles exhibit such electrical phenomena. The result of this electro-physiological activity is the presence of various bio-electric voltages (i.e., bio-potentials) that exist throughout the body and on its surface. The surface signals are routinely recorded and interpreted to provide non-invasive information regarding the physiological state of an individual.
In the heart, for example, electrical signals coordinate the rhythmic pumping of the cardiac muscles and the bio-potential signals resulting from the heart's electrical activity are routinely recorded. This record of the well-coordinated electrical events that take place within the heart is called an electrocardiogram (ECG).
The brain also exhibits electrical activity that occurs mainly in the cerebral cortex. The electric potentials, measured on the scalp, are called brain waves and the recorded brain activity, as a function of time, is called an electroencephalogram (EEG). Under many conditions, multiple neurons within the cortex fire simultaneously producing an asynchronous signal with little information content. However, when the input to a region in the brain is synchronous with the electrical activity occurring at the same time, rhythmic EEG signals, with various amplitude and frequency content, are obtained from different regions of the brain. Such regions include the frontal, occipital, temporal, and parietal lobes.
Clinically, the EEG and ECG techniques are both currently used to diagnose a number of physiological conditions. In the clinical ECG, three to twelve electrodes are attached to the chest to obtain detailed information related to the state and condition of the heart. The status of heart muscles (e.g., potential ischemia) is often determined and various life-threatening heart arrhythmias are routinely identified. In the case of the clinical EEG, up to twenty-six (or more) electrodes are attached to the patient's scalp and forehead. The resulting EEG bio-potential signals are examined as a means to indicate diseased brain tissue, and identify potential brain tumors. EEG has also been used extensively to diagnose sleep disorders, and in the diagnosis and treatment of specific types of epileptic conditions. There is also a desire to obtain EEG signals from patients suspected of having a stroke as the EEG data could provide an early indication of the type of stroke. This information could also help select and guide specific treatment modalities.
Monitoring the small-amplitude EEG and ECG signals currently requires use of contact electrodes that are physically attached to the body surface. Further, an electrolyte gel is needed as an interface between the skin and the electrode material. The gel provides what is often referred to as a wet contact with low electrical impedance. The low impedance is required to minimize noise pickup from the surrounding environment as well as small movements from the individual.
Currently, there are a number of companies that provide a variety of ECG instruments for medical research and clinical practice. Use of the ECG is especially widespread and the equipment is highly advanced. There are sophisticated diagnostic ECG instruments, monitoring devices for routine use for a variety of medical environments and even portable (i.e., credit-card size) devices. The portable instruments are used for ambulatory ECG monitoring as well as in fitness and exercise programs.
Evaluation of ECG data is relatively straightforward and highly advanced. With little training, most medical staff can obtain a good deal of information from the ECG signals. Automated, computer analysis is available to assist the Cardiologist in diagnosing various heart abnormalities. Because of the nature and convenience of obtaining and interpreting the ECG signals, almost every patient in an operating room (OR), intensive care unit (ICU), or ER environment is routinely monitored with ECG equipment.
Equipment for EEG monitoring is also available from several manufacturers. The recording of EEG bio-potentials is, on the other hand, currently reserved more for research purposes and in some specific diagnostic situations. EEG data is only sporadically used for monitoring in the ER/ICU environment. Because of the complex nature of the multiple EEG signals, a specialist must normally analyze EEG measurements.
Recently a device, called the BIS (Bispectral Index) monitor has been introduced that uses EEG signals to determine a patient's hypnotic state in the OR environment. In this case one sensor comprised of three disposable electrodes is coated with electrolyte gel and attached to the patients' forehead. A special electronics unit provides a single, macro-EEG output that is indicative of the state of anesthetic hypnosis. This output corresponds to a numeric unit from 0-100 indicating an absence of brain activity to maximum brain activity respectively.
Shortcomings in the current ECG and EEG measurement approaches are mainly related to electrode/electrolyte gel attachment. In the ECG case, the electrode (with electrolyte gel) is kept in contact with the skin using a special, disposable adhesive patch. The electrodes are relatively simple to attach and easy to remove. If body hair is present, however, attachment and removal can be problematic. In most cases, good ECG recordings can be obtained, but the attachment site must be on bare skin (i.e., the upper-body clothing must be removed) and the electrode attachment site often must be cleaned using rubbing alcohol. Up to twelve electrodes are used for detailed diagnosis of the heart's electrophysiology, but only two or three are needed for general monitoring of the heart in an operating room (OR), intensive care unit (ICU), or emergency room (ER). Finally, most medical staff can quickly and correctly attach an ECG electrode with a minimum amount of operator training.
Attachment of EEG electrodes, on the other hand, introduces a new set of problems to medical staff wanting to use this technology, namely:
1) The electrodes are often made of materials such as gold or silver preventing routine disposal. This means that the electrodes must be cleaned before and after use by each patient.
2) The patients' scalp must be cleaned using a relatively strong solvent, such as acetone, and mildly abraded prior to application of the cup-shaped electrode filled with electrolyte paste.
3) New electrolyte gel must be applied manually to the electrode prior to attachment for each new patient.
4) Pressure must be applied to the gel-filled electrode-cup assembly to cause adherence to the head. This process is often uncomfortable for the patient.
5) The contact resistance of the electrode to the scalp must often be measured to insure it is less than 1000 ohms otherwise noisy recordings are obtained. This measurement process is time consuming and tedious.
6) During use, the electrolyte gel tends to harden and stick to the hair of the patient. Removal of the electrodes and remnants of the gel from the hair takes some time and effort with much discomfort to the patient.
During use, the electrodes often became dislodged requiring re-attachment. Such difficulties result in the following:
1) A trained technical staff person is normally required to attach the electrodes. Often this technician is not available at all times, so the clinician cannot depend on obtaining the desired EEG data.
2) There is an additional cost factor associated with using trained staff and the current medical reimbursement policies tend to encourage minimal use of trained staff in the hospital environment.
3) The attachment protocol takes a considerable amount of time especially when multiple electrodes are required.
4) The ordeal is difficult and tedious for the patient.
Because of the cost and inconvenience of applying EEG electrodes, it is difficult (if not impossible) to use the EEG for routine patient monitoring. EEG information is, therefore, not normally obtained in the ICU, or ER environment.
Use of Magnetic Resonance Imaging (MRI) machines has become a routine method for obtaining information regarding a patient's anatomy and physiology. Currently, however, not many patients are monitored (except some children) while they are in the MRI using EEG and/or ECG instrumentation. Basically, the MRI and EEG/ECG equipment are not compatible. The operating MRI produces strong radio frequency (RF) fields and large static magnetic fields are always present. These fields induce current flow in electrodes and any attached electrode wires especially if the wires are inadvertently formed in a loop. Some instances of localized skin burns have been reported or a result of electrodes and looped wires residing in MRI machines. Such cases are recognized as macro shock situations, whereby current distribution is diffused throughout the body. Such situations can be fatal if the current induced is sufficiently large.
The presence of equipment near the MRI machine can also interfere with the diagnostic quality of the MRI images themselves by causing distortions in the MRI output. Also, the radio-frequency (RF) fields of the MRI machine can corrupt the weak signals being recorded by ECG equipment and especially even weaker signals associated with EEG instruments. For this reason, a special screen room is built around the MRI machine to prevent it from affecting equipment in the vicinity of the imaging device. Generally, MRI test patients have all electrodes removed from their body and all unnecessary equipment is kept outside the MRI screen room.
To solve these and other associated problems with prior art bio-potential measuring electrodes, it is an object of the present invention to provide a device that avoids a macro shock situation.
It is an object of the present invention to provide easy set up for measuring bio-potentials.
It is an object of the present invention to optimize a patient's comfort level during the bio-potential measurement process.
Also, it is an object of the present invention to eliminate the use of electrolytic paste during bio-potential measurement.
It is an object of the present invention to minimize patient preparation for bio-potential measurement.
It is an object of the present invention to avoid patient removal of hair or clothes.
It is an object of the present invention to provide standard clinicians and hospital employees with a bio-potential measurement device that is easy to use without extensive training.
It is an object of the present invention to provide multiple small sized bio-potential sensors that can be fit into small areas.
It is an object of the present invention to minimize electromagnetic interference (EMI) noise.
It is an object of the present invention to provide a bio-potential measuring instrument with low power consumption.
It is an object of the present invention to provide a bio-potential device that can be used at various frequencies.
It is an object of the present invention to provide an output that interfaces with standard amplifiers, filters, hardware devices, and computer software.
It is an object of the present invention to provide a bio-potential sensor that is re-useable.